Petroleum casing pipe with high strength, high toughness and large strain performance and preparation method thereof

Abstract

The invention discloses a petroleum casing pipe with high strength, high toughness and large strain performance and a preparation method thereof, and belongs to the technical field of casing pipe preparation for oil and gas exploitation. According to the petroleum casing pipe with the high strength, the high toughness and the large strain performance, alloy elements Mn, Si, Cr, Ni, Mo, Al, Nb and V are added into medium-low C for microalloying, in addition, the content of harmful elements such as P, S, O, H and N is controlled, and the final components can meet the requirements of oil and gas wells under complex working conditions for the large strain casing pipe; related experimental results prove that the yield strength of the oil casing with the high strength, the high toughness and the large strain performance reaches the level of 110 ksi, the level of 125 ksi and the level of 140 ks respectively, the yield ratio is smaller than or equal to 0.89-0.93, the uniform elongation is larger than or equal to 15%-20%, and the oil casing can meet the practical requirements of complex working conditions in oil and gas wells.

Description

Technical Field

[0001] The invention belongs to the technical field of casing preparation for oil and gas development, and in particular relates to a petroleum casing with high strength, high toughness and large strain performance and a preparation method thereof. Background Art

[0002] With the development of the world's oil and gas industry, the environment for oil and gas exploration and development is becoming increasingly complex. Deep sea, deep layer, low permeability, shale oil and gas, and old oil fields are currently the focus of development. There are more and more special structure wells such as directional wells and large displacement wells. Most shale oil and gas and low permeability oil and gas wells need to be transformed to increase production. Casing deformation often occurs during well construction, reaching 30% to 50% in severe cases, resulting in the inability to seat the bridge plug in place, reducing the number of fracturing stages, reducing the production of a single well, and shortening the life of the oil and gas well. When the casing is severely deformed, the drilling and plugging operation cannot be completed, and even the wellbore integrity fails.

[0003] Studies have shown that the main failure mechanism of casing is deformation caused by shear and crushing stress. The main controlling factors mainly depend on the relative size and distribution of the bearing capacity of the casing string and the external load. It is related to the material properties and structural dimensions of the casing itself, formation conditions (natural ground fissures, formation heterogeneity), and fracturing operation parameters (pressure, displacement, number of times, etc.). The load factors are mainly internal and external pressure, axial tension and compression, bending, additional stress caused by fracturing pressure and its temperature changes, uneven ground stress, fault slip, natural fracture expansion, hydraulic fracture expansion, etc. and mutual interference. In addition to optimizing the wellbore trajectory (controlling formation conditions), optimizing the fracturing process (improving fracturing load conditions), and adopting a new method of wellbore integrated coordinated deformation to alleviate casing deformation, it is very important to improve the bearing capacity of the casing string. The bearing capacity of the casing is manifested in the material strength (steel grade), structural strength (material strength and structural size), toughness (brittle fracture resistance), and uniform deformation resistance (yield strength ratio-the ratio of yield strength to its tensile strength, uniform elongation) of the casing.

[0004] The traditional casing string design method is based on stress design, which requires the working stress to be lower than the yield strength of the material, that is, the casing (column) is not allowed to undergo plastic deformation during use. But in fact, due to the changes in the curvature and azimuth of the wellbore, the wellbore trajectory is an irregular spatial shape, and the implementation of production-enhancing measures such as fracturing transformation will cause local plastic deformation of the casing, which puts forward requirements for the plastic deformation capacity (yield strength ratio, uniform elongation) of the casing, that is, to control the plastic deformation of the casing within the allowable range, so as to ensure the safety of the deformed casing, that is, to adopt a strain-based casing (column) design, which also proposes the development and application of casings with high strength, high toughness and large strain performance.

[0005] So far, except for the high-strain casing used in heavy oil steam thermal recovery wells, there are few reports on the application of high-strain casing in the world. For N80 and below steel grade casing, although the strain-based casing string design method is not adopted, and no requirements are put forward for the strain performance of the casing, due to its low strength and high elongation (including uniform elongation), most casings can easily meet the requirements of the large strain performance of the casing based on the strain-based casing string design method. However, for P110 and above steel grade casing, due to the phenomenon that its strength, plasticity and toughness are in a state of trade-off, it is often difficult to meet the requirements at the same time. In fact, a large part of the yield strength ratio of P110 and above steel grade casing exceeds 0.93, and some even reach 0.98. Too high a yield strength ratio will lead to a significant decrease in the uniform plastic deformation capacity of the material, and seriously reduce the safety of use. According to relevant research results and engineering experience, it is proposed to control the yield strength ratio of the casing below 0.93 or even lower to meet the needs of the safe use of the casing string based on the strain design method. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a petroleum casing with high strength, high toughness and large strain performance and a preparation method thereof, so as to solve the technical problem that the existing casing cannot meet the large strain requirements of oil and gas wells under complex working conditions.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The invention discloses a petroleum casing with high strength, high toughness and large strain performance. The components of the petroleum casing include, by mass percentage, C: 0.23%-0.29%, Si: 0.65%-0.85%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%, Cr: 0.90%-1.20%, Ni: 0.30%-0.50%, Mo: 0.25%-0.35%, Al: 0.07%-0.12%, Ca: 0.016%-0.024%, O+H+N≤0.008%, Nb: 0.04%-0.09% or V: 0.04%-0.09%, and the balance is Fe and other inevitable impurities.

[0009] The present invention also discloses a method for preparing the above-mentioned petroleum casing with high strength, high toughness and large strain performance, comprising the following steps:

[0010] S1: After steelmaking treatment and adding modified components, the components of the obtained molten steel are the components of the oil casing as claimed in claim 1;

[0011] S2: continuously casting the molten steel to obtain a rod-shaped continuous casting billet;

[0012] S3: heating the rod-shaped continuous casting billet and then performing piercing, followed by hot continuous rolling to obtain a pre-treated casing;

[0013] S4: After heat treatment and post-treatment of the pretreated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained.

[0014] Furthermore, in S1, the steelmaking process adopts electric furnace steelmaking or oxygen-blown converter steelmaking; the electric furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

[0015] Furthermore, in S1, after adding the modifying components, refining outside the furnace and vacuum degassing are performed to obtain molten steel.

[0016] Furthermore, in S2, the continuous casting process uses electromagnetic stirring and soft reduction technology to control the center segregation of the rod-shaped continuous casting billet.

[0017] Furthermore, in S3, the heating temperature of the rod-shaped continuous casting billet is 1185-1215°C, and the heating time is 90-120 min; the temperature during the piercing is 1150-1200°C; the temperature of the hot rolling is 1000-1130°C; after the hot rolling, it is cooled in air to obtain a pretreated sleeve.

[0018] Further, in S4, the heat treatment is a heat treatment process using a protective atmosphere furnace for heating, quenching and high temperature tempering;

[0019] The quenching process parameters are: quenching temperature of 900-920°C, holding time of 50-70min, internal and external water spray quenching, cooling rate ≥30°C / s;

[0020] The process parameters of the high temperature tempering are as follows: the high temperature tempering temperature is 570° C. to 650° C., and the high temperature tempering time is 90 to 120 minutes.

[0021] Furthermore, in S4, after the heat treatment and post-treatment, the pre-treated sleeve needs to be subjected to heat straightening, tempering and water cooling treatment in sequence; the temperature of the heat straightening is 520°C to 600°C; the temperature of the tempering is 520°C to 600°C, and the time is 90 to 120 minutes.

[0022] Furthermore, after water cooling treatment, thread processing is performed to obtain a petroleum casing with high strength, high toughness and large strain performance.

[0023] Furthermore, the thread processing is processing API standard threads or special threads on the pipe section.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention discloses a petroleum casing with high strength, high toughness and large strain performance. The alloy elements Mn, Si, Cr, Ni, Mo, Al, Nb and V are added to the medium and low C for microalloying. The medium and low carbon content of 0.23% to 0.29% is beneficial to improving the plasticity and toughness of the steel. However, too low carbon content is not conducive to improving the hardenability of the steel and is not conducive to improving the strength of the steel. Too high carbon content is not conducive to improving the plasticity and toughness of the steel. Based on the above C content, Mn, Si, Cr, Ni, Mo, Al, Nb and V are introduced for combined strengthening, so that the hardenability of the steel is improved and the strength is improved, and the influence on the yield strength ratio is small. At the same time, the hardenability and tempering stability of the steel are improved, and the strength of the steel is improved. The hardenability of the steel is improved, thereby improving the strength. Its addition can also improve the plasticity and toughness of the steel. Among them, Al combines with oxygen or nitrogen to form fine and uniformly distributed oxides or nitrides, which can play the role of refining grains and improving strength and toughness at the same time, and is also important. V is added to the steel to form VC and VN with C and N in the steel, which has the effect of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness; Nb is added to the steel to form NbC and NbN with C and N in the steel, which has the effect of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness; Ca is added to the steel to improve the properties and morphology of inclusions, thereby improving the plasticity and toughness of the steel, and the effect is better when Ca / S≥2; in addition, the content of harmful elements such as P, S, O, H, and N is controlled so that the final composition can meet the needs of large strain casings in complex working conditions of oil and gas wells; according to relevant experimental results, the yield strength of the oil casing with high strength, high toughness and large strain performance of the above-mentioned composition reaches 110ksi, 125ksi, and 140ks respectively, the yield strength ratio is ≤0.89~0.93, and the uniform elongation is ≥15~20%, which can meet the practical needs of complex working conditions in oil and gas wells.

[0026] The present invention also discloses a method for preparing the above-mentioned oil casing with high strength, high toughness and large strain performance. After adopting creative component design, continuous casting, perforation, heat treatment and post-treatment are carried out to obtain fine and uniform tempered troostite, thereby reducing the influence of residual stress on casing performance, so that the prepared oil casing has excellent mechanical properties and can meet the needs of oil and gas wells with complex working conditions for high-strength and large-strain casing. The preparation method is simple to operate and easy to realize industrial production. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0029] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0030] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0031] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0032] The present invention provides a petroleum casing with high strength, high toughness and large strain performance. In order to ensure that the requirements of the strain-based casing string design method for casing strength, toughness, and large strain performance (yield strength ratio, uniform elongation) are met, its chemical composition and manufacturing process must be reasonably designed.

[0033] In terms of composition design, it is planned to use medium and low C, add alloying elements Mn, Si, Cr, Ni, Mo, Al, Nb, V micro-alloying, control harmful elements such as P, S, O, H, N in the steel, fully deoxidize Al-Si, and treat the molten steel with Ca; increase the content of Mn and Si elements which have less effect on the yield ratio.

[0034] The functions and content ranges of the main elements are as follows:

[0035] C: It is the main strengthening element in steel. Using medium and low carbon is beneficial to improving the plasticity and toughness of steel, but too low carbon content is not conducive to improving the hardenability of steel and is not conducive to improving the strength of steel; too high carbon content is not conducive to improving the plasticity and toughness of steel. It is advisable to control it within the range of 0.23% to 0.29%.

[0036] Si: It has a solid solution strengthening effect in steel and has little effect on the yield strength ratio. It is also an important deoxidizer. It is best to control it within the range of 0.65% to 0.85%.

[0037] Mn: Mn is dissolved in steel to improve the hardenability and strength of steel and has little effect on the yield strength ratio. It is best to control it within the range of 1.30% to 1.50%.

[0038] Cr: Cr is dissolved in steel to improve the hardenability and tempering stability of steel, thereby increasing the strength of steel. However, too high a content will increase the cost. It is best to control it within the range of 0.90% to 1.20%.

[0039] Ni: It is dissolved in steel to improve the hardenability and strength of steel. Its addition can also improve the plasticity and toughness of steel, but too high a content will increase the cost. It is better to control it within the range of 0.30% to 0.50%.

[0040] Mo: Mo is dissolved in steel to improve the hardenability and tempering stability of steel, thereby improving the strength of steel. At the same time, adding Mo can inhibit the segregation of Mn and P, improve uniformity, and improve the temper brittleness of steel. The effect is better when Mo / P≥15, but too high a content will increase the cost. It is best to control it within the range of 0.25% to 0.35%.

[0041] Al: Combined with oxygen or nitrogen to form fine and evenly distributed oxides or nitrides, it can refine the grains and improve strength and toughness. It is also an important deoxidizer and nitrogen fixer, but too much content will affect the hot working properties of steel. It is best to control it within the range of 0.07% to 0.12%.

[0042] V: added to steel to form VC and VN with C and N in steel, which has the effect of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness. However, too high a content will cause excessive VC and VN content, which will damage the plasticity and toughness of the steel and increase the cost. It is best to control it within the range of 0.04% to 0.09%.

[0043] Nb: Added into steel to form NbC and NbN with C and N in steel, it has the function of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness. However, too high a content will cause excessive NbC and NbN content, which will damage the plasticity and toughness of the steel and increase the cost. It is advisable to control it within the range of 0.04% to 0.09%.

[0044] Ca: Adding Ca into steel can improve the properties and morphology of inclusions, thereby improving the plasticity and toughness of steel. The effect is better when Ca / S ≥ 2. It is best to control it within the range of 0.016% to 0.024%.

[0045] P: Harmful element, mainly affecting the plasticity and toughness of steel. It is advisable to control P ≤ 0.015%.

[0046] S: Harmful element, mainly affecting the plasticity and toughness of steel. It is advisable to control S ≤ 0.005%.

[0047] O, H, and N are harmful elements that mainly affect the plasticity and toughness of steel. It is advisable to control O+H+N≤0.008%.

[0048] In summary, the composition of the large strain casing is as follows by mass percentage: C: 0.23% ~ 0.29%, Si: 0.65% ~ 0.85%, Mn: 1.30% ~ 1.50%, P ≤ 0.015%, S ≤ 0.005%, Cr: 0.90% ~ 1.20%, Ni: 0.30 ~ 0.50%, Mo: 0.25% ~ 0.35%, Nb: 0.04% ~ 0.09% or V: 0.04% ~ 0.09%, Al: 0.07% ~ 0.12%, Ca: 0.016% ~ 0.024%, O + H + N ≤ 0.008%, and the balance is Fe and other inevitable impurities.

[0049] The present invention also discloses a method for preparing the above-mentioned petroleum casing, which mainly adopts processes such as steelmaking (including refining outside the furnace and vacuum degassing), continuous casting, hot rolling in the austenite zone, heat treatment, heat straightening, stress relief tempering, etc., so that the material obtains a fine and uniform microstructure to achieve a reasonable match between the material strength, plasticity and toughness; in order to control the yield strength, the final rolling temperature is increased, a higher hot straightening temperature is adopted, and measures such as stress relief tempering are adopted.

[0050] The specific steps include:

[0051] S1: After steelmaking treatment and adding modified components, the components of the obtained molten steel are the components of the oil casing as claimed in claim 1;

[0052] S2: continuously casting the molten steel to obtain a rod-shaped continuous casting billet;

[0053] S3: heating the rod-shaped continuous casting billet and then performing piercing, followed by hot continuous rolling to obtain a pre-treated casing;

[0054] S4: After heat treatment and post-treatment of the pretreated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained.

[0055] Preferably, in terms of the tube preparation process, the material is mainly made to obtain a fine and uniform microstructure through processes such as steelmaking (including refining outside the furnace, vacuum degassing), continuous casting, hot rolling in the austenite zone, heat treatment, hot straightening, stress relief and tempering, so as to achieve a reasonable match between the material strength, plasticity and toughness; in order to control the yield strength, the final rolling temperature is increased, a higher hot straightening temperature is adopted, and measures such as stress relief and tempering are adopted.

[0056] Preferably, the steps include:

[0057] ① Steelmaking: batching, electric furnace or oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain the above-mentioned molten steel with the composition of the oil casing.

[0058] ②Continuous casting: The molten steel is cast into a rod-shaped continuous casting billet, and a continuous casting process is adopted. During the continuous casting process, electromagnetic stirring and light pressure reduction technology are used to control the center segregation of the continuous casting billet.

[0059] ③ Piercing and hot rolling: The obtained rod-shaped continuous casting billet is heated in a ring heating furnace with a heating furnace temperature of 1185℃~1215℃ and a heating time of 90~120min, hot pierced at 1150℃~1200℃, hot rolled at 1000℃~1130℃, then air cooled and sawed to a suitable length. Using a higher final rolling temperature is conducive to obtaining a lower yield strength ratio and a larger uniform plastic deformation elongation.

[0060] ④ Heat treatment and post-treatment: adopt the heat treatment process of heating in protective atmosphere furnace, quenching + high temperature tempering. The quenching temperature should be controlled at 900℃~920℃, the holding time is 50~70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s, to ensure that basically all martensite structures are obtained after quenching; the tempering temperature is controlled at 570℃~650℃, the tempering time is 90~120min, in order to obtain fine and uniform tempered troostite, the grain size is 8 or finer, and water cooling is performed after tempering to avoid possible temper brittleness. After heat treatment, hot straightening is performed, the straightening temperature is controlled at 520℃~600℃, and then water cooling is performed. In order to reduce the influence of residual stress on the performance of the casing, tempering is performed at 520℃~600℃ and 90~120 minutes after hot straightening, and water cooling is performed after tempering. Then non-destructive testing is performed.

[0061] ⑤Thread processing: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0062] The oil casing with high strength, high toughness and large strain performance obtained by the present invention through appropriate preparation technology has excellent comprehensive performance, and its yield strength level can reach 110ksi, 125ksi and 140ksi requirements respectively, that is, the room temperature yield strength is greater than 758-965MPa, the tensile strength is greater than 862-1034MPa, the yield strength ratio is ≤0.89-0.93, the total elongation is ≥15-20%, the uniform elongation is ≥10-15%, and the Charpy impact toughness is ≥80-100J. It can meet the needs of oil and gas wells with complex working conditions for high-strength and large-strain casing.

[0063] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0064] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0065] Example 1

[0066] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0067] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0068] The composition of the molten steel, in percentage by mass, includes: C: 0.24%, Si: 0.70%, Mn: 1.32%, P: 0.010%, S: 0.003%, Cr: 0.90%, Ni: 0.33%, Mo: 0.27%, V: 0.04%, Al: 0.09%, Ca: 0.016%, O+H+N: 0.007%, and the balance is Fe and other inevitable impurities;

[0069] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0070] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0071] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃±10℃, the holding time is 50min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 640℃±10℃, the tempering time is 90min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 590℃±10℃, and then water cooling; after hot straightening, tempering is carried out at 590℃±10℃, 90min, and water is used after tempering, and then non-destructive testing is carried out;

[0072] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0073] The oil casing with high strength, high toughness and large strain performance obtained in Example 1 has a room temperature yield strength greater than 861 MPa, a tensile strength greater than 978 MPa, a yield strength ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 105 J.

[0074] Example 2

[0075] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0076] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0077] The composition of the molten steel, in terms of mass percentage, includes: C: 0.23%, Si: 0.65%, Mn: 1.30%, P: 0.011%, S: 0.002%, Cr: 0.96%, Ni: 0.30%, Mo: 0.31%, V: 0.044%, Al: 0.07%, Ca: 0.019%, O+H+N: 0.005%, and the balance is Fe and other inevitable impurities;

[0078] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0079] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0080] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 50min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 640℃110℃, the tempering time is 90min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 590℃110℃, and then water cooling; after hot straightening, tempering is carried out at 590℃110℃, 90min, and water is used after tempering, and then non-destructive testing is carried out;

[0081] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0082] The oil casing with high strength, high toughness and large strain performance obtained in Example 2 has a room temperature yield strength greater than 853 MPa, a tensile strength greater than 958 MPa, a yield strength ratio of 0.89, a total elongation of 24%, a uniform elongation of 17%, and a Charpy impact toughness of 113 J.

[0083] Example 3

[0084] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0085] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0086] The composition of the molten steel, in percentage by mass, includes: C: 0.26%, Si: 0.72%, Mn: 1.37%, P: 0.008%, S: 0.002%, Cr: 1.03%, Ni: 0.35%, Mo: 0.32%, V: 0.051%, Al: 0.08%, Ca: 0.021%, O+H+N: 0.006%, and the balance is Fe and other inevitable impurities;

[0087] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0088] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0089] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 50min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 640℃110℃, the tempering time is 90min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 590℃110℃, and then water cooling; after hot straightening, tempering is carried out at 590℃110℃, 90min, and water is used after tempering, and then non-destructive testing is carried out;

[0090] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0091] The oil casing with high strength, high toughness and large strain performance obtained in Example 3 has a room temperature yield strength greater than 856 MPa, a tensile strength greater than 962 MPa, a yield strength ratio of 0.89, a total elongation of 24%, a uniform elongation of 17%, and a Charpy impact toughness of 117 J.

[0092] Example 4

[0093] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0094] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0095] The composition of the molten steel, in percentage by mass, includes: C: 0.25%, Si: 0.73%, Mn: 1.35%, P: 0.0111%, S: 0.002%, Cr: 0.93%, Ni: 0.37%, Mo: 0.32%, V: 0.056%, Al: 0.10%, Ca: 0.020%, O+H+N: 0.005%, and the balance is Fe and other inevitable impurities;

[0096] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0097] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0098] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 50min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 640℃110℃, the tempering time is 90min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 590℃110℃, and then water cooling; after hot straightening, tempering is carried out at 590℃110℃, 90min, and water is used after tempering, and then non-destructive testing is carried out;

[0099] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0100] The oil casing with high strength, high toughness and large strain performance obtained in Example 4 has a room temperature yield strength greater than 869 MPa, a tensile strength greater than 988 MPa, a yield strength ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 108 J.

[0101] Example 5

[0102] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0103] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0104] The composition of the molten steel, in percentage by mass, includes: C: 0.27%, Si: 0.72%, Mn: 1.38%, P: 0.008%, S: 0.002%, Cr: 0.98%, Ni: 0.40%, Mo: 0.29%, V: 0.062%, Al: 0.11%, Ca: 0.022%, O+H+N: 0.004%, and the balance is Fe and other inevitable impurities;

[0105] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0106] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0107] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 50min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 640℃110℃, the tempering time is 90min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 590℃110℃, and then water cooling; after hot straightening, tempering is carried out at 590℃110℃, 90min, and water is used after tempering, and then non-destructive testing is carried out;

[0108] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0109] The oil casing with high strength, high toughness and large strain performance obtained in Example 5 has a room temperature yield strength greater than 865 MPa, a tensile strength greater than 983 MPa, a yield strength ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 119 J.

[0110] Example 6

[0111] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0112] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0113] The composition of the molten steel, in percentage by mass, includes: C: 0.24%, Si: 0.68%, Mn: 1.36%, P: 0.009%, S: 0.003%, Cr: 1.06%, Ni: 0.45%, Mo: 0.30%, V: 0.080%, Al: 0.10%, Ca: 0.018%, O+H+N: 0.006%, and the balance is Fe and other inevitable impurities;

[0114] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0115] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0116] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 60min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 610℃110℃, the tempering time is 100min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 560℃110℃, and then water cooling; after hot straightening, tempering is performed at 560℃110℃, 100min, and water is used after tempering, and then non-destructive testing is performed;

[0117] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0118] The oil casing with high strength, high toughness and large strain performance obtained in Example 6 has a room temperature yield strength greater than 951 MPa, a tensile strength greater than 1045 MPa, a yield strength ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 109 J.

[0119] Example 7

[0120] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0121] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0122] The composition of the molten steel, in percentage by mass, includes: C: 0.27%, Si: 0.71%, Mn: 1.44%, P: 0.010%, S: 0.003%, Cr: 1.09%, Ni: 0.37%, Mo: 0.28%, V: 0.083%, Al: 0.09%, Ca: 0.020%, O+H+N: 0.005%, and the balance is Fe and other inevitable impurities;

[0123] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0124] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0125] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 60min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 610℃110℃, the tempering time is 100min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 560℃110℃, and then water cooling; after hot straightening, tempering is performed at 560℃110℃, 100min, and water is used after tempering, and then non-destructive testing is performed;

[0126] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0127] The oil casing with high strength, high toughness and large strain performance obtained in Example 7 has a room temperature yield strength greater than 959 MPa, a tensile strength greater than 1054 MPa, a yield strength ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 106 J.

[0128] Example 8

[0129] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0130] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0131] The composition of the molten steel, in percentage by mass, includes: C: 0.25%, Si: 0.65%, Mn: 1.39%, P: 0.012%, S: 0.003%, Cr: 1.03%, Ni: 0.43%, Mo: 0.26%, V: 0.070%, Al: 0.10%, Ca: 0.017%, O+H+N: 0.007%, and the balance is Fe and other inevitable impurities;

[0132] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0133] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0134] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 60min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 610℃110℃, the tempering time is 100min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 560℃110℃, and then water cooling; after hot straightening, tempering is performed at 560℃110℃, 100min, and water is used after tempering, and then non-destructive testing is performed;

[0135] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0136] The oil casing with high strength, high toughness and large strain performance obtained in Example 8 has a room temperature yield strength greater than 944 MPa, a tensile strength greater than 1049 MPa, a yield strength ratio of 0.90, a total elongation of 20%, a uniform elongation of 14%, and a Charpy impact toughness of 93 J.

[0137] Example 9

[0138] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0139] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0140] The composition of the molten steel, in percentage by mass, includes: C: 0.26%, Si: 0.71%, Mn: 1.42%, P: 0.010%, S: 0.003%, Cr: 1.01%, Ni: 0.40%, Mo: 0.33%, V: 0.074%, Al: 0.09%, Ca: 0.023%, O+H+N: 0.006%, and the balance is Fe and other inevitable impurities;

[0141] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0142] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0143] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 60min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 610℃110℃, the tempering time is 100min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 560℃110℃, and then water cooling; after hot straightening, tempering is performed at 560℃110℃, 100min, and water is used after tempering, and then non-destructive testing is performed;

[0144] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0145] The oil casing with high strength, high toughness and large strain performance obtained in Example 9 has a room temperature yield strength greater than 947 MPa, a tensile strength greater than 1052 MPa, a yield strength ratio of 0.90, a total elongation of 20%, a uniform elongation of 14%, and a Charpy impact toughness of 98 J.

[0146] Example 10

[0147] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0148] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0149] The composition of the molten steel, in percentage by mass, includes: C: 0.28%, Si: 0.65%, Mn: 1.37%, P: 0.012%, S: 0.002%, Cr: 1.05%, Ni: 0.39%, Mo: 0.31%, V: 0.09%, Al: 0.11%, Ca: 0.018%, O+H+N: 0.007%, and the balance is Fe and other inevitable impurities;

[0150] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0151] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0152] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 60min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 610℃110℃, the tempering time is 100min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 560℃110℃, and then water cooling; after hot straightening, tempering is performed at 560℃110℃, 100min, and water is used after tempering, and then non-destructive testing is performed;

[0153] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0154] The oil casing with high strength, high toughness and large strain performance obtained in Example 10 has a room temperature yield strength greater than 954 MPa, a tensile strength greater than 1048 MPa, a yield strength ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 102 J.

[0155] Embodiment 11

[0156] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0157] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0158] The composition of the molten steel, in percentage by mass, includes: C: 0.26%, Si: 0.75%, Mn: 1.45%, P: 0.009%, S: 0.003%, Cr: 1.1%, Ni: 0.46%, Mo: 0.48%, Nb: 0.053%, Al: 0.10%, Ca: 0.021%, O+H+N: 0.005%, and the balance is Fe and other inevitable impurities;

[0159] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0160] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0161] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 580℃110℃, the tempering time is 120min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 530℃110℃, and then water cooling; after hot straightening, tempering is carried out at 530℃110℃, 120min, and water is used after tempering, and then non-destructive testing is carried out;

[0162] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0163] The oil casing with high strength, high toughness and large strain performance obtained in Example 11 has a room temperature yield strength greater than 1051 MPa, a tensile strength greater than 1142 MPa, a yield strength ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 89 J.

[0164] Example 12

[0165] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0166] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0167] The composition of the molten steel, in percentage by mass, includes: C: 0.25%, Si: 0.77%, Mn: 1.43%, P: 0.010%, S: 0.001%, Cr: 1.20%, Ni: 0.45%, Mo: 0.35%, Nb: 0.090%, Al: 0.12%, Ca: 0.019%, O+H+N: 0.006%, and the balance is Fe and other inevitable impurities;

[0168] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0169] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0170] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 580℃110℃, the tempering time is 120min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 530℃110℃, and then water cooling; after hot straightening, tempering is carried out at 530℃110℃, 120min, and water is used after tempering, and then non-destructive testing is carried out;

[0171] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0172] The oil casing with high strength, high toughness and large strain performance obtained in Example 12 has a room temperature yield strength greater than 1047 MPa, a tensile strength greater than 1126 MPa, a yield strength ratio of 0.93, a total elongation of 18%, a uniform elongation of 12%, and a Charpy impact toughness of 93 J.

[0173] Embodiment 13

[0174] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0175] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0176] The composition of the molten steel, in percentage by mass, includes: C: 0.28%, Si: 0.70%, Mn: 1.50%, P: 0.008%, S: 0.001%, Cr: 1.13%, Ni: 0.50%, Mo: 0.32%, Nb: 0.066%, Al: 0.09%, Ca: 0.024%, O+H+N: 0.004%, and the balance is Fe and other inevitable impurities;

[0177] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0178] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0179] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 580℃110℃, the tempering time is 120min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 530℃110℃, and then water cooling; after hot straightening, tempering is carried out at 530℃110℃, 120min, and water is used after tempering, and then non-destructive testing is carried out;

[0180] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0181] The oil casing with high strength, high toughness and large strain performance obtained in Example 12 has a room temperature yield strength greater than 1045 MPa, a tensile strength greater than 1124 MPa, a yield strength ratio of 0.93, a total elongation of 18%, a uniform elongation of 12%, and a Charpy impact toughness of 85 J.

[0182] Embodiment 14

[0183] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0184] S1: batching, electric furnace steelmaking, feeding Si-Ca wire to modify the inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0185] The composition of the molten steel, in percentage by mass, includes: C: 0.27%, Si: 0.85%, Mn: 1.46%, P: 0.010%, S: 0.003%, Cr: 1.15%, Ni: 0.48%, Mo: 0.34%, Nb: 0.040%, Al: 0.11%, Ca: 0.020%, O+H+N: 0.005%, and the balance is Fe and other inevitable impurities;

[0186] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0187] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0188] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 580℃110℃, the tempering time is 120min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 530℃110℃, and then water cooling; after hot straightening, tempering is carried out at 530℃110℃, 120min, and water is used after tempering, and then non-destructive testing is carried out;

[0189] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0190] The oil casing with high strength, high toughness and large strain performance obtained in Example 14 has a room temperature yield strength greater than 1054 MPa, a tensile strength greater than 1146 MPa, a yield strength ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 87 J.

[0191] Embodiment 15

[0192] A method for preparing a petroleum casing having high strength, high toughness and large strain performance comprises the following steps:

[0193] S1: batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to denature inclusions in the steel, refining outside the furnace and vacuum degassing to obtain molten steel with the following composition;

[0194] The composition of the molten steel, in percentage by mass, includes: C: 0.29%, Si: 0.72%, Mn: 1.48%, P: 0.008%, S: 0.003%, Cr: 1.18%, Ni: 0.47%, Mo: 0.33%, Nb: 0.078%, Al: 0.10%, Ca: 0.022%, O+H+N: 0.006%, and the balance is Fe and other inevitable impurities;

[0195] S2: Continuously casting the molten steel to obtain a rod-shaped continuous casting billet; electromagnetic stirring and soft pressure reduction technology are used during the continuous casting process to control the center segregation of the continuous casting billet;

[0196] S3: heating the rod-shaped continuous casting billet in a ring heating furnace at a heating furnace temperature of 1200115°C for 100 min, hot piercing at 1150°C-1200°C, hot continuous rolling at 1000°C-1130°C, air cooling, and sawing to a suitable length to obtain a pre-treated casing;

[0197] S4: After heat treatment and post-treatment of the pre-treated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained; wherein, the heat treatment and post-treatment adopt a heat treatment process of heating in a protective atmosphere furnace, quenching + high temperature tempering, the quenching temperature is 910℃110℃, the holding time is 70min, the internal and external water spray quenching, the cooling rate is ≥30℃ / s; the tempering temperature is 580℃110℃, the tempering time is 120min, and the tempering is followed by water cooling; after heat treatment; hot straightening and stress relief tempering are also required in the middle, the straightening temperature is controlled at 530℃110℃, and then water cooling; after hot straightening, tempering is carried out at 530℃110℃, 120min, and water is used after tempering, and then non-destructive testing is carried out;

[0198] S5: According to user requirements, API standard threads or special threads can be processed on the pipe section, and the threads can be subjected to magnetic particle inspection.

[0199] The oil casing with high strength, high toughness and large strain performance obtained in Example 15 has a room temperature yield strength greater than 1059 MPa, a tensile strength greater than 1151 MPa, a yield strength ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 96 J.

[0200] In the above embodiments, the steelmaking process adopts electric furnace steelmaking or oxygen-blown converter steelmaking; the electric furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

[0201] Table 1 shows the chemical composition of the oil casings of Examples 1 to 15 with yield strength levels of 110 ksi, 125 ksi, and 140 ksi, respectively. In each example, the balance is Fe and unavoidable impurities.

[0202] Table 1 Chemical composition of oil casing in the embodiment

[0203] serial number C Si Mn P S Cr Ni Mo Nb V Al Ca O+H+N 1(110ksi) 0.24 0.70 1.32 0.010 0.003 0.90 0.33 0.27 - 0.040 0.09 0.016 0.007 2(110ksi) 0.23 0.65 1.30 0.011 0.002 0.96 0.30 0.31 - 0.044 0.07 0.019 0.005 3(110ksi) 0.26 0.72 1.37 0.008 0.002 1.03 0.35 0.25 - 0.051 0.08 0.021 0.006 4(110ksi) 0.25 0.73 1.35 0.011 0.002 0.93 0.37 0.32 - 0.056 0.10 0.020 0.005 5(110ksi) 0.27 0.72 1.38 0.008 0.002 0.98 0.40 0.29 - 0.062 0.11 0.022 0.004 6(125ksi) 0.24 0.68 1.36 0.009 0.003 1.06 0.45 0.30 - 0.080 0.10 0.018 0.006 7(125ksi) 0.27 0.71 1.44 0.010 0.003 1.09 0.37 0.28 - 0.083 0.09 0.020 0.005 8(125ksi) 0.25 0.65 1.39 0.012 0.003 1.03 0.43 0.26 - 0.070 0.10 0.017 0.007 9(125ksi) 0.26 0.71 1.42 0.010 0.003 1.01 0.40 0.33 - 0.074 0.09 0.023 0.006 10(125ksi) 0.28 0.65 1.37 0.012 0.002 1.05 0.39 0.31 - 0.090 0.11 0.018 0.007 11(140ksi) 0.26 0.75 1.45 0.009 0.003 1.10 0.46 0.48 0.053 - 0.10 0.021 0.005 12(140ksi) 0.25 0.77 1.43 0.010 0.001 1.20 0.45 0.35 0.090 - 0.12 0.019 0.006 13(140ksi) 0.28 0.70 1.50 0.008 0.001 1.13 0.50 0.32 0.066 - 0.09 0.024 0.004 14(140ksi) 0.27 0.85 1.46 0.010 0.003 1.15 0.48 0.34 0.040 - 0.11 0.020 0.005 15(140ksi) 0.29 0.72 1.48 0.008 0.003 1.18 0.47 0.33 0.078 - 0.10 0.022 0.006

[0204] Table 2 shows the parameters of the casing materials of Examples 1 to 15 after appropriate preparation processes, which have excellent comprehensive properties such as strength, plasticity, and toughness: room temperature yield strength 853-1059 MPa, tensile strength 958-1151 MPa, yield strength ratio 0.88-0.93, total elongation 17-24%, uniform elongation 11-17%, and Charpy impact toughness 85-119 J at 0°C. It can meet the needs of oil and gas wells with complex working conditions for high-strength and high-strain casings.

[0205] Table 2 Heat treatment process and performance of oil casing in Example

[0206]

[0207] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A petroleum casing with high strength, high toughness and large strain performance, characterized in that: The components of the oil casing include, by mass percentage, C: 0.23%-0.29%, Si: 0.65%-0.85%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%, Cr: 0.90%-1.20%, Ni: 0.30%-0.50%, Mo: 0.25%-0.35%, Al: 0.07%-0.12%, Ca: 0.016%-0.024%, O+H+N≤0.008%, Nb: 0.04%-0.09% or V: 0.04%-0.09%, and the balance is Fe and other inevitable impurities.

2. The method for preparing a petroleum casing having high strength, high toughness and large strain performance as claimed in claim 1, characterized in that: The following steps are involved: S1: After steelmaking treatment and adding modified components, the components of the obtained molten steel are the components of the oil casing as claimed in claim 1; S2: continuously casting the molten steel to obtain a rod-shaped continuous casting billet; S3: heating the rod-shaped continuous casting billet and then performing piercing, followed by hot continuous rolling to obtain a pre-treated casing; S4: After heat treatment and post-treatment of the pretreated casing, a petroleum casing with high strength, high toughness and large strain performance is obtained.

3. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S1, the steelmaking process adopts electric furnace steelmaking or oxygen-blown converter steelmaking; the electric furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

4. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S1, after adding the modifying components, refining outside the furnace and vacuum degassing are carried out to obtain molten steel.

5. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S2, the continuous casting process uses electromagnetic stirring and soft reduction technology to control the center segregation of the rod-shaped continuous casting billet.

6. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S3, the heating temperature of the rod-shaped continuous casting billet is 1185-1215°C, and the heating time is 90-120 minutes; the temperature during the piercing is 1150-1200°C; the temperature of the hot rolling is 1000-1130°C; after the hot rolling, it is cooled in air to obtain a pretreated sleeve.

7. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S4, the heat treatment is a heat treatment process using a protective atmosphere furnace for heating, quenching and high temperature tempering; The quenching process parameters are: quenching temperature of 900-920°C, holding time of 50-70min, internal and external water spray quenching, cooling rate ≥30°C / s; The process parameters of the high temperature tempering are as follows: the high temperature tempering temperature is 570° C. to 650° C., and the high temperature tempering time is 90 to 120 minutes.

8. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 2, characterized in that: In S4, after the pretreatment sleeve is heat treated and post-treated, it is also necessary to perform heat straightening, tempering and water cooling treatment in sequence; the temperature of the heat straightening is 520°C to 600°C; the temperature of the tempering is 520°C to 600°C, and the time is 90 to 120 minutes.

9. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 8, characterized in that: After water cooling treatment, thread processing is performed to obtain a petroleum casing with high strength, high toughness and large strain performance.

10. The method for preparing a petroleum casing having high strength, high toughness and large strain performance according to claim 9, characterized in that: The thread processing is processing API standard threads or special threads on the pipe section.

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